The invention relates to a telecommunication system and method, wherein a binder of subscriber lines extends between a switch and a plurality of user terminals and far-end crosstalk cancellation is provided.
Such system and method is provided in connection with xDSL-systems, offering broadband internet connections via existing telephone lines.
In existing xDSL-systems comprising binders of a large number of copper subscriber lines, the major disadvantage of significant crosstalk results in a limitation of the system performance and quality of broadband transmissions (QoS), in particular a limitation of the achievable data rates.
In FIG. 1, a typical structure of a state of the art telephone network is shown. At their respective origin in switches (central offices or cabinets, respectively) the telephone lines are part of large binders, which, with increasing distance from the origin, are more and more branched into smaller binders, until single telephone lines (or a very small binder) end at a single user (subscriber) and are connected to his transceiver terminal.
As a practical matter, there exists non-negligable crosstalk between the several lines where the lines are coiled in binders.
FIG. 2 is an illustration of the topology of such crosstalk for N Telephone lines. Numerals CO0 to CON represent the xDSL transmitting and receiving means in the central office or the cabinet, respectively. CPE0 and CPEN represent xDSL modems of the users. The crosstalk has to be differentiated into near-end crosstalk (NEXT) and far-end crosstalk (FEXT).
It is a well-known physical phenomenon that, in principle, the achievable data rate of closely neighboured electrical subscriber lines may be limited by crosstalk. This is in particular valid for data transmission according to the most recent xDSL-Standard, since VDSL/VDSL2-systems use the frequency range up to 30 MHz, and crosstalk is considerably increased at such high frequencies. On the other hand, the channel losses are much higher at higher frequencies than at lower frequencies. This results in the effect that especially over relatively short transmission distances the achievable data rate is limited by the amount of crosstalk between the subscriber lines of a binder.